The invention relates to improving the potency, absorption or pharmacokinetic properties of therapeutic compounds to certain vitamin D forms. Vitamin D plays a role in calcium, phosphate, and bone homeostasis. The hormonal activity of vitamin D is mediated through binding to the vitamin D receptor (VDR). It enters the nucleus where it binds to the vitamin D receptor element (VDRE) present in the promoters of a subset of genes that are thus responsive to hormonal Vitamin D.
Vitamin D is a group of fat-soluble secosteroids. Several forms (vitamers) of vitamin D exist. The two major forms are vitamin D2 or ergocalciferol, and vitamin D3 or cholecalciferol. Vitamin D without a subscript refers to vitamin D2, D3 or other forms known in the art. In humans, vitamin D can be ingested as cholecalciferol (vitamin D3) or ergocalciferol (vitamin D2). The major source of vitamin D for most humans is sunlight. Once vitamin D is made in the skin or ingested, it needs to be activated by a series of hydroxylation steps, first to 25-hydroxyvitamin D (25(OH)D3) in the liver and then to 1,25-dihydroxyvitamin D3 (1α,25(OH)2D3) in the kidney. 1α,25(OH)2D3 is the active “hormonal” form of vitamin D because it binds to VDR. 25(OH)D3 is the “non-hormonal” form of vitamin D and is the major circulating form in the human body. It binds the vitamin D Binding Protein (DBP). It is only converted to the hormonal form as needed. An example of a non-hormonal vitamin D form is one that lacks a 1α-hydroxyl group. Non-hormonal vitamin D forms have a greatly reduced affinity for VDR and a greatly increased affinity for DBP.
DBP is the principal transporter of vitamin D metabolites. Its concentration in the plasma is 6-7 μM and has been detected in all fluid compartments. DBP concentrations exceed the physiological vitamin D metabolite concentrations. DBP is important for the translocation of vitamin D from the skin into circulation, and across cell membranes into the cytoplasm where vitamin D is activated into the hormonal form. The affinity of non-hormonal Vitamin D for DBP is significantly higher than the affinity of the hormonal form. In contrast, the affinity of the hormonal form to VDR is significantly than the non-hormonal form.
Vitamin D and vitamin D analogs have been approved for the treatment of osteoporosis and secondary hyperparathyroidism. Vitamin D has also been shown to inhibit proliferation and induce differentiation in normal as well as cancer cells. The level of vitamin D required for this activity causes severe toxicity in the form of hypercalcemia. Analogs of vitamin D have been approved for the treatment of psoriasis and others are currently being tested for cancer treatment. Many of the analogs discovered to have a reduced calcemic effect contain side-chain modifications. These modifications do not greatly affect VDR binding, and thus, in cell-based proliferation assays, show equal or even increased efficacy. It was shown, however, that many of these modifications reduce binding to DBP and thereby reduce the half-life in the bloodstream.
The addition of poly(ethylene glycol) or (PEG) is a known method of increasing the half-life of some compounds by reducing kidney clearance, reducing aggregation, and diminishing potentially unwanted immune recognition (Jain, Crit. Rev. Ther. Drug Carrier Syst. 25:403-447 (2008)). The PEG is typically used at a considerably large size (20-40 kDa) to maximize the half-life in circulation. This can be accomplished by using either a single large PEG or multiple smaller PEGs attached to the compound. (Clark et al. J. Biol. Chem. 271:21969-21977 (1996); Fishburn, J. Pharm. Sci. 97:4167-4183 (2008)).
Absorption is a primary focus in drug development and medicinal chemistry because a drug must be absorbed before any medicinal effects can take place. A drug's absorption profile can be affected by many factors. Additionally, the absorption properties of therapeutic compounds vary significantly from compound to compound. Some therapeutic compounds are poorly absorbed following oral or dermal administration. Other therapeutic compounds, such as most peptide- and protein-based therapeutics, cannot be administered orally. Alternate routes of administration such as intravenous, subcutaneous, or intramuscular injections are routinely used for some of these compounds; however, these routes often result in slow absorption and exposure of the therapeutic compounds to enzymes that can degrade them, thus requiring much higher doses to achieve efficacy.
A number of peptides have been identified as therapeutically promising. The chemical and biological properties of peptides and proteins make them attractive candidates for use as therapeutic compounds. Peptides and proteins are naturally-occurring molecules made up of amino acids and are involved in numerous physiological processes. Peptides and proteins display a high degree of selectivity and potency, and may not suffer from potential adverse drug-drug interactions or other negative side effects. Thus peptides and proteins hold great promise as a highly diverse, highly potent, and highly selective class of therapeutic compounds with low toxicity. Peptides and proteins, however, may have short in vivo half-lives. For such peptides, this may be a few minutes. This may render them generally impractical, in their native form (also referred to as “wild”, “wild type” or “wt” herein), for therapeutic administration. Additionally, peptides may have a short duration of action or poor bioavailability.
Apelin peptide (SEQ ID NO:1) is encoded by the APLN gene. The apelin gene encodes a pre-proprotein of 77 amino acids with a signal peptide in the N-terminal region. After translocation into the endoplasmic reticulum and cleavage of the signal peptide, the proprotein of 55 amino acids may generate several active fragments: a 36 amino acid peptide corresponding to the sequence 42-77 (apelin 36), a 17 amino acid peptide corresponding to the sequence 61-77 (apelin 17) and a 13 amino acid peptide corresponding to the sequence 65-77 (apelin 13). This latter fragment may also undergo a pyroglutamylation at its N-terminal glutamine residue.
Apelin is the endogenous ligand for the G-protein-coupled APJ receptor that is expressed at the surface of some cell types. It is widely expressed in various organs such as the heart, lung, kidney, liver, adipose tissue, gastrointestinal tract, brain, adrenal glands, endothelium, and human plasma.
The apelin receptor participates in the control of blood pressure and the formation of new blood vessels (angiogenesis). Apelin causes hypotension from the activation of its receptors on the surface of endothelial cells. This induces the release of NO, a potent vasodilator, which induces relaxation of the smooth muscle cells of artery wall. The angiogenic activity results from Apelin promoting the proliferation and migration of endothelial cells and the formation of new blood vessels. Other effects of apelin include regulation of fluid homeostasis, hypothalamic regulation of food and water intake, pituitary hormone release, and down-regulation of the antidiuretic hormone vasopressin in the brain. Additionally, apelin is secreted in the gastrointestinal tract and in the pancreas.
Apelin regulates cardiovascular and fluid homeostasis, food intake, cell proliferation, and angiogenesis. Apelin is also considered to be an adipokine that is linked to metabolic disorders such as obesity and type 2 diabetes. Apelin therapies may thus be a beneficial treatment for these conditions. See, e.g., Castan-Laurell, et al., Endocrine 40(1):1-9 (2011). Indeed, Apelin inhibits insulin secretion induced by glucose. Likewise, insulin stimulates apelin, revealing a feedback loop for insulin production. The in vivo half-life of apelin, however, is 20 minutes or less. See, e.g., Bertrand et al. Front Physiol. 6:115 (2015).
Ghrelin is a mammalian peptide (SEQ ID NO:2) that is naturally secreted from the stomach into circulation to stimulate appetite and release of growth hormone (GH). Ghrelin stimulates the release of growth hormone from the pituitary gland through the cellular receptor GHS-R and plays an important role in energy homeostasis. In addition, ghrelin acts directly on the central nervous system to decrease sympathetic nerve activity. GHS-Rs are concentrated in the hypothalamus-pituitary unit. GHS-R is distributed in peripheral tissues, including the heart, lung, liver, kidney, pancreas, stomach, small and large intestines, adipose, and immune cells.
Ghrelin has been used therapeutically to increase weight and lean body mass in patients suffering from cachexia or involuntary weight loss resulting from chronic diseases such as cancer (Hiura et. al., Cancer, 118:4785-94 (2012)). Ghrelin, however, has a naturally short half-life of 11 minutes in humans (Akamizu et al., Eur J Endocrinol 150:447-55 (2004)) and thus must be dosed often to see therapeutic effects.
Parathyroid hormone (PTH), parathormone or parathyrin, is secreted by the chief cells of the parathyroid glands. It is a polypeptide containing 84 amino acids (SEQ ID NO:10). It acts to increase the concentration of calcium (Ca2+) in the blood (in contrast to calcitonin which decreases calcium concentration). PTH activates the parathyroid hormone 1 receptor (bone and kidney) and the parathyroid hormone 2 receptor (central nervous system, pancreas, testis, and placenta). PTH, however, has a very short half-life of approximately 4 minutes.
Hypoparathyroidism is a low level of PTH in the blood that is most commonly due to damage to or removal of parathyroid glands during thyroid surgery, immune system-related damage, inheritance, or other rare causes. It can lead to low levels of calcium in the blood, often causing cramping and twitching of muscles or tetany (involuntary muscle contraction), and several other symptoms. Calcium replacement or vitamin D can ameliorate the symptoms but can increase the risk of kidney stones and chronic kidney disease. See, e.g. Winer K K, et. al. J. Clin. Endocrinol. Metab. 97(2): 391-399 (2012).
Insulin is a peptide hormone produced by beta cells in the pancreas that regulates the metabolism of carbohydrates and fats (SEQ ID NO:11 and 12). The human insulin protein is composed of 51 amino acids, and has a molecular weight of 5808 Daltons. It is a dimer of an A-chain and a B-chain that are linked by disulfide bonds. It promotes the absorption of glucose from the blood to skeletal muscles and fat tissue and causes fat to be stored rather than used for energy.
Under normal physiological conditions, insulin is produced at a constant proportion to remove excess glucose from the blood. When control of insulin levels fails, however, diabetes mellitus can result. Thus, diabetic patients often receive injected insulin. Patients with type 1 diabetes depend on external insulin for their survival because the hormone is no longer sufficiently produced internally. Insulin is most commonly injected subcutaneously. Patients with type 2 diabetes are often insulin resistant and may suffer from an “apparent” insulin deficiency.
Fibroblast Growth Factor 21 (SEQ ID:2) is a protein that circulates in serum. Encoded by the FGF21 gene, it is a member of a family of atypical fibroblast growth factors (FGFs) that includes FGF19 and FGF23. It lacks the conventional FGF heparin-binding domain. FGF family members possess broad mitogenic and cell survival activities and are involved in a variety of biological processes including embryonic development, cell growth, morphogenesis, tissue repair, tumor growth and invasion. FGF21 is specifically induced by HMGCS2 activity. FGF21 stimulates glucose uptake in adipocytes but not in other cell types. This effect is additive to the activity of insulin.
FGF21 prefers binding to the FGFR1c/b-Klotho receptor complex over those containing other FGFR isotypes (Kliewer and Mangelsdorf, Am. J. Clin. Nutr. 91:254S-257S (2010)). Administration of FGF21 to diabetic animals reduces circulating glucose levels while excess FGF21 does not induce hypoglycemia as seen with administration of excess insulin (Kharitonenkov and Shanafelt, Curr. Opin. Investig. Drugs 10:359-364 (2009)). Therefore, FGF21 is a promising therapeutic protein for the treatment of diabetes. FGF21 in its natural state, however, has an extremely short half-life in serum (about 1.1 hours) making it a clinically impractical treatment (see, e.g. WO03/011213; Kharitonenkov et al., J Clin. Invest. 115:1627-1635 (2005)). Additionally, FGF21 exhibits poor bioavailability when injected subcutaneously (Xu J et al., 2009. Am J Physiol. Endocrinol. Metab. 297: E1105-E1114).
Infliximab (Remicade®, Janssen Biotech Inc., U.S. Pat. No. 5,919,452 and US 2002/0141996, incorporated herein by reference in their entirety) is a monoclonal antibody that binds tumor necrosis factor alpha (TNF-α, SEQ ID NO:13) that is used to treat autoimmune diseases. Infliximab was approved by the U.S. Food and Drug Administration (FDA) for the treatment of psoriasis, Crohn's disease, ankylosing spondylitis, psoriatic arthritis, rheumatoid arthritis, and ulcerative colitis. TNF-α is a chemical messenger (cytokine) and a key part of the autoimmune reaction. Infliximab is administered intravenously by a healthcare professional and is not approved for subcutaneous dosing.
RNA interference (RNAi) is a process where RNA molecules inhibit gene expression often by causing specific mRNA molecules to degrade. Two types of RNA molecules—microRNA (miRNA) and small interfering RNA (siRNA)—are central to RNA interference. They bind to the target mRNA molecules and either increase or decrease their activity. RNAi helps cells defend against parasitic nucleic acids such as those from viruses and transposons. RNAi also influences development.
Initial medical applications for RNAi involve genetic diseases such as macular degeneration and Huntington's disease. Additional applications may include certain cancers, respiratory syncytial virus, herpes simplex virus type 2, HIV, hepatitis A and B, influenza, and measles.
It remains difficult to deliver RNAi to target tissues, and in particular, tissues deep within the body. siRNA molecules have a short in vivo half-life due to endogenous nucleases. Also, targeting specific tissues is challenging. One approach has been high dosage levels of siRNA to ensure the tissues have been reached. With these approaches, however, hepatotoxicity was reported.
Therapeutic oligonucleotides, while promising, suffer from a short plasma half-life as well as from problems with delivery and cellular uptake. Conjugation of oligonucleotides to small molecules has been proposed to overcome these problems but have not yet been successful.